SKELETAL ALTERATIONS IN HYPOPHYSECTOMIZED RATS .1. A HISTOMORPHOMETRIC STUDY ON TIBIAL CANCELLOUS BONE

Background: Hypophysectomy (HX) results in a cessation of bone growth and a decrease in bone metabolism, The purpose of this study is to exa mine the effect of HX on the static and dynamic histomorphometry of ca ncellous bone in the secondary spongiosa of the proximal tibial metaph ysis in rats. Methods: Female rats, at 2 or 3 months of age, were HX a nd sacrificed at 0, 5 days, 2 and 5 weeks after the surgery. Age-match ed intact rats served as controls. Cancellous bone histomorphometry wa s performed on double-fluorescent labeled, 30-um-thick sections of the proximal tibia, Tartrate-resistant acid phosphatase histomorphometry was performed at 5 days on HX and control rats to evaluate the resorpt ion in the metaphyseal bone. Results: Although the intact rats gained in body weight, tibial length, tibial weight, and density after 5 week s, these changes did not occur following HX, As compared to the basal group, HX resulted in a decrease in the density and dry weight of the metaphysis. The histomorphometric data showed that the cancellous bone volume and trabecular number of the secondary spongiosa were decrease d and the separation was increased in the HX rats. The dynamic results showed that HX significantly decreased longitudinal growth rate and t issue-based bone formation and resorption. However, the bone surface-b ased eroded surface, labeled surface, the mineral apposition rate, and the bone formation rate did not differ between the intact and the HX rats at either the 2 or 5 weeks study. Five days after HX, the bone su rface and tissue-based osteoclast surfaces were significantly lower in the HX than in the intact rats. Conclusions: Pituitary hormone defici ency results in cancellous bone loss. The bone loss is due primarily t o the suppression of longitudinal growth-dependent bone gain and the i nhibition of tissue-based bone turnover with a lower bone formation re lative to bone resorption. The surface-based bone turnover is not affe cted. (C) 1995 Wiley-Liss, Inc.